The Espresso Machine

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Generating Pressure

EM 2.01 The ‘Bike Pump’ Approach

Throughout the nineteenth century and well into the early twentieth, machine designers and the public seemed to share a conviction that steam was an essential part of achieving great coffee flavour. These days we know this to be untrue — on a modern machine, steam comes in direct contact only with milk, never with coffee grinds. Moreover, brewers such as stovetop coffee makers that do use steam to push water through a coffee bed tend to produce bitter-tasting brews. Nonetheless, it took manufacturers a bit of time to debunk the myth of steam. 

The first convincing attempt to generate pressure without using steam, by means of hand pumps, resulted in a handful of interesting patents. But in terms of the family tree of coffee machines, air pressure machines never grew into a large branch. The problem is that air is extremely compressible, whereas water is not compressible at all. As such, water pressure turns out to be a much simpler and more efficient means of generating high pressure.  

An experiment from our Immersion course demonstrates the limitations of air pressure for espresso purposes: We determine the maximum amount of pressure you can obtain when using an AeroPress. As the video below shows, with a very hard push, we were unable to generate even 0.5 bar of pressure. AeroPresses produce outstanding filter coffee, but they do not create crema, and they cannot extract coffee efficiently at high brew ratios (i.e., where you use a lot of coffee and a small amount of water). 

How much pressure can you generate in an AeroPress with your hardest plunge? We find out in this video where we have fitted a pressure gauge into the plunger of an AeroPress.


Hand Pumps

Luigi Giarlotto, of Turin, Italy, made the breakthrough in 1909 with the first known pump machine fitted with a water pump and an air pump. Giarlotto would certainly have been aware of Moriondo’s machines. His new design featured a large group head, very similar to the one on Moriondo’s machine,